From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752025AbdG0OdP (ORCPT ); Thu, 27 Jul 2017 10:33:15 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:56295 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751941AbdG0OdN (ORCPT ); Thu, 27 Jul 2017 10:33:13 -0400 Date: Thu, 27 Jul 2017 07:33:08 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com Subject: Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Reply-To: paulmck@linux.vnet.ibm.com References: <1500933497-12612-4-git-send-email-paulmck@linux.vnet.ibm.com> <20170725163318.bporqvcoodtel4a6@hirez.programming.kicks-ass.net> <20170725164900.GR3730@linux.vnet.ibm.com> <20170725165957.alykngbnrrwn3onw@hirez.programming.kicks-ass.net> <20170725171701.GS3730@linux.vnet.ibm.com> <20170725185320.uis4hxqaqlx7y7gp@hirez.programming.kicks-ass.net> <20170725193612.GW3730@linux.vnet.ibm.com> <20170727101426.gvbympkitoqyvfxj@hirez.programming.kicks-ass.net> <20170727125659.GO3730@linux.vnet.ibm.com> <20170727133729.syymgkfslzam732w@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170727133729.syymgkfslzam732w@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17072714-0048-0000-0000-000001CA8D2C X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007435; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000214; SDB=6.00893668; UDB=6.00446799; IPR=6.00673828; BA=6.00005495; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00016408; XFM=3.00000015; UTC=2017-07-27 14:33:11 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17072714-0049-0000-0000-00004207B1D7 Message-Id: <20170727143308.GV3730@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-07-27_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1706020000 definitions=main-1707270229 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 27, 2017 at 03:37:29PM +0200, Peter Zijlstra wrote: > On Thu, Jul 27, 2017 at 05:56:59AM -0700, Paul E. McKenney wrote: > > On Thu, Jul 27, 2017 at 12:14:26PM +0200, Peter Zijlstra wrote: > > > On Tue, Jul 25, 2017 at 12:36:12PM -0700, Paul E. McKenney wrote: > > > > This horse is already out, so trying to shut the gate won't be effective. > > > > > > So I'm not convinced it is. The mprotect() hack isn't portable as we've > > > established and on x86 where it does work, it doesn't (much) perturb > > > tasks not related to our process because we keep a tight mm_cpumask(). > > > > Wrong. People are using it today, portable or not. If we want them > > to stop using it, we need to give them an alternative. Period. > > What's wrong? The mprotect() hack isn't portable, nor does it perturb > other users much. > > I would much rather they use this than your > synchronize_sched_expedited() thing. Its much better behaved. And > they'll run into pain the moment they start using ARM,PPC,S390,etc.. What is wrong is that we currently don't provide them a reasonable alternative. Thanx, Paul